When the stepping motor is used for controlling the stitches, a load torque of a motor should be lower than a generated torque thereof for preventing the stepping motor from going out of service. However, although this condition is satisfied under the normal driving state, the mechanism is made heavy due to, e.g., exposure in the low temperatures, and the load torque is increased, and then if the motor were driven at high speed, it would be out of order.
With respect to a build of the stepping motor and a control thereof, a surplus or room may be kept therefore, but a cost is increased or responsibility at high speed is sacrificed.